Every marathon runner knows the feeling of hitting a wall – when legs grow heavy, breath becomes ragged, and that coveted finish time seems to slip away. While we often blame pre-race jitters, high humidity, or even our diet, new research suggests a less obvious culprit might be at play: the very air we breathe.
A groundbreaking study by Brown University researchers analyzed millions of marathon finish times from major U.S. races over 17 years. Their findings reveal a direct link between higher levels of fine particulate matter, known as PM2.5, and slower completion times. PM2.5 refers to microscopic pollutants, less than 2.5 micrometers in diameter, that frequently trigger air quality warnings. For instance, in New York State, concentrations of 35 micrograms per cubic meter are enough to prompt a health advisory.
The study, which encompassed nine marathons including those in New York City, Boston, and Los Angeles between 2003 and 2019, showed a clear pattern: for every increase of one microgram per cubic meter of these tiny particles, men’s average finish times were 32 seconds slower, and women’s were 25 seconds slower. This means that on even a moderately polluted day, your marathon time could be minutes slower. Data consistently illustrated that more pollution correlated with slower marathon times across these events.
As Joseph M. Braun, a professor of epidemiology at Brown University’s School of Public Health, noted, “What’s remarkable is that we’re looking at people who are all incredibly healthy. But even among really healthy people, air pollution is having an important, albeit subtle, effect on your physiology.”
This particulate pollution primarily stems from the combustion of fossil fuels in power plants, vehicle exhaust, and events like forest fires or waste incineration. Even brief exposure to PM2.5 can be detrimental, as these minuscule particles can penetrate deep into the lungs and bloodstream, leading to inflammation, coughing, or chest tightness. For individuals with existing health conditions, it can worsen asthma or bronchitis and even precipitate strokes or heart attacks.
While air quality in many parts of the U.S. has improved due to pollution regulations, there’s growing concern over sudden spikes, particularly from wildfire smoke that increasingly blankets regions across the continent. Additionally, recent governmental actions have sought to roll back various environmental regulations, including limits on emissions from vehicles and industrial smokestacks.
To assess pollution levels, the researchers utilized machine-learning models that estimated PM2.5 concentrations along marathon routes on specific race days, drawing data from monitoring stations. They found that the Los Angeles Marathon generally exhibited the highest median pollution levels, coinciding with the slowest median finish times. While other factors like warmer temperatures and a notoriously hilly course might contribute to slower times in Los Angeles, the overall trend of reduced performance in more polluted races remained consistent across the 2.6 million finish times analyzed, even when comparing different years within the same city.
Intriguingly, the study challenged the idea that elite runners might be more resilient to environmental stressors. In fact, the performance dip was more pronounced for faster-than-average marathoners, possibly because their increased breathing rate leads to higher pollution intake. “Even a microgram-per-cubic-meter-lower PM2.5 level on race day could be the difference between breaking a record, or not,” Professor Braun emphasized.
Beyond air quality, heat and humidity also pose significant challenges for runners. A separate analysis of 221 marathons by Climate Central, a nonprofit research group, revealed that the ideal cool temperatures for peak performance are becoming increasingly rare as global temperatures rise. Furthermore, the chronic impact of living and training in polluted areas could indirectly affect marathon times by limiting an individual’s ability to train intensely.
Carlos Gould, an environmental health scientist at the University of California, San Diego, who was not involved in the study, commended the researchers for their meticulous work in isolating pollution’s effects amidst numerous other variables. “It’s more evidence that air pollution really affects every part of our lives,” he stated.
Jack McNamara, a New York-based creative director training for the upcoming marathon, reflected on his own concerns about air quality while running along Manhattan’s busy West Side Highway. His awareness heightened after Canadian wildfires cast a smoky haze over the city in 2023. He foresees a future where runners might increasingly choose races in cities known for their cleaner air. “Running a marathon is such an extreme activity, I think people look for every single edge and advantage they can get,” he said. For those participating in the New York marathon this Sunday, there’s good news: the air quality forecast is currently favorable.